Reliability of phases retrieved from 400-kV spot-scan images of purple membranes acquired on a slow-scan CCD camera

Glucose-embedded purple membranes were used as a test specimen to evaluate the reliability of phases retrieved from 400-kV spot-scan images acquired on a 1024 × 1024 slow-scan CCD camera. This specimen was chosen because it represents a broad class of low-contrast radiation-sensitive biological objects and its structure is well established. The amplitudes of computed reflections from these images were strongly damped by the modulation transfer function of the camera. Nevertheless, their phases on average were < 12° different from the reference data of Henderson et al . (1986), Ultramicroscopy , 19 , 147–178, up to 8.8 Å resolution, which corresponds to 0.8 of the Nyquist frequency of the camera.